perturbation

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The act of perturbing.
2. n. The state of being perturbed; agitation.
3. n. A small change in a physical system.
4. n. Physics & Astronomy Variation in a designated orbit, as of a planet, resulting from the influence of one or more external bodies.

Century Dictionary and Cyclopedia

1. n. The act of perturbing, or the state of being perturbed; disturbance; disorder; especially, disquiet of mind; restlessness or want of tranquillity of mind; commotion of the passions.
2. n. Variation; especially, irregular or violent variation.
3. n. A cause of disquiet.
4. n. In astronomy, a deviation of the motion of a planet or comet from a fixed orbit or from its regular velocity in that orbit. Perturbations are caused by the gravitating action of bodies other than the primary or central body. They are commonly and conveniently conceived, not as drawing the planets out of their orbits, but as consisting in gradual changes of the elements of the orbits themselves. All perturbations due to gravitation are, strictly speaking, periodical. But some of them, which depend upon the relative situation of the orbits of different planets, go through their changes in such vast intervals of time that they are more conveniently regarded as progressive and not periodic, and are termed secular perturbations; while others, depending for the most part upon the relative situations of the planets in their orbits, go through their changes in comparatively short intervals of time, and can only be represented as periodic, and these are technically called the periodic inequalities.

Wiktionary

1. n. uncountable Agitation; the state of being perturbed
2. n. countable A small change in a physical system, or more broadly any definable system (such as a biological or economic system)
3. n. countable, astronomy, physics Variation in an orbit due to the influence of external bodies

GNU Webster's 1913

1. n. The act of perturbing, or the state of being perturbed; esp., agitation of mind.
2. n. (Astron.) A disturbance in the regular elliptic or other motion of a heavenly body, produced by some force additional to that which causes its regular motion.

WordNet 3.0

1. n. a disposition that is confused or nervous and upset
2. n. (physics) a secondary influence on a system that causes it to deviate slightly
3. n. activity that is a malfunction, intrusion, or interruption
4. n. the act of causing disorder
5. n. an unhappy and worried mental state